JP2010008654A - Organic el image display - Google Patents

Abstract

An active matrix organic EL image display device capable of meeting a plurality of requirements such as downsizing, high luminance and high accuracy image quality is provided.
[Solution]
A plurality of pixels arranged in a matrix on a substrate, a plurality of scanning lines and a plurality of signal lines arranged to cross each of the pixels, and a plurality of pixels arranged in parallel with the signal lines In the image display device, each pixel includes a first transistor, a storage capacitor, a second transistor, and an organic EL element that emits light by current supplied from the power supply line. In the plurality of pixels, pixel rows of odd types of colors are sequentially arranged in the extending direction of the scanning lines, and the power supply line is a pixel row of two colors among the pixel rows of odd types of colors. And a single power supply line for supplying current to a pixel row of one color.
[Selection] Figure 7

Description

  The present invention relates to an active matrix image display device that is used in a personal computer, a cellular phone, and the like and has a light emitting element and a transistor.

  2. Description of the Related Art Conventionally, an organic EL image display device using a current control type organic EL (Electroluminescence) element that emits light by recombination of holes and electrons injected into a light emitting layer has been proposed.

  In this organic EL image display device, a thin film transistor (hereinafter abbreviated as TFT) formed of amorphous silicon, polycrystalline silicon, or the like formed on a substrate, the above-described organic EL element, or the like constitutes each pixel. The luminance is controlled by setting an appropriate current value for each pixel.

  Specifically, a plurality of pixels arranged in a matrix on a substrate, a scanning line that supplies a scanning signal to each pixel, and a data signal for luminance that is arranged so as to intersect the scanning line are distributed to each pixel. And a power supply line for energizing each pixel.

  Next, a conventional circuit in each pixel will be described with reference to FIG. This pixel circuit includes an organic light emitting element OLED, a drive transistor Td, a threshold voltage detection transistor Tth, and a storage capacitor Cs. The scanning line 20 is connected to the gate of the threshold detection transistor Tth, the signal line 30 is connected to the storage capacitor Cs, the anode side of the organic light emitting diode OLED is connected to the power supply line 40, and the cathode side is connected to the drain of the driving transistor Td and the threshold value. The drains of the voltage detection transistors Tth are connected to each other. Based on the amount of current applied to the gate of the driving transistor, a current flows through the organic EL element (organic EL light emitting diode) OLED to emit light (see, for example, Patent Document 1).

The organic EL image display device is required to have a plurality of performances such as downsizing, high luminance and high accuracy image quality. In order to respond to this, among the pixels arranged in a matrix, one circuit arrangement of two adjacent pixels is reversed in order in a direction orthogonal to the feed line, and is arranged symmetrically around the feed line. A technique is disclosed in which two adjacent pixel columns are energized with one power supply line. As a result, compared with the case where the power supply line is formed for each pixel group in one column, the area where the power supply line is formed can be narrowed, so that the function of the pixel circuit can be enhanced. In the case of the bottom emission type, the light emission region of the pixel can be expanded, and the luminance can be improved (see, for example, Patent Document 2).
JP 2004-252110 A Japanese Patent Laid-Open No. 11-24606

  However, the organic EL image display device has the following problems. For example, when the above-described technique is used for pixels in which the pixels have an odd number of color types including three colors of red, green, and blue, and these are sequentially arranged in a direction orthogonal to the feeder line 40, red, The blue and green pixels are sequentially inverted.

  The thin film transistors of the drive transistor Td and the threshold voltage detection transistor Tth are formed by photolithography, but when the photomask is misaligned during the formation of the thin film transistor, the characteristics of the normal pixel and the inverted pixel differ. Will be formed. As a result, for example, odd-numbered normal pixels become bright and even-numbered pixels become dark. Here, since the three pixels in the picture element are arranged in red, green, and blue, the normal pixel circuit arrangement is (normal) and the inverted pixel circuit arrangement is (inverted) in the direction orthogonal to the feed line. When the arranged pixels are shown in order, one picture element [red (normal), green (inverted), blue (normal)], two picture elements [red (inverted), green (normal), blue (inverted)] ...

  In the above, when red single color display is performed, the odd-numbered picture elements are brightened and the even-numbered picture elements are darkened, so that vertical stripes are visually recognized every other row of picture elements. In addition, when white display is performed, red and blue pixels are lightened in odd-numbered pixels, and magenta is obtained because the green pixels are dark, and green pixels are lightened in even-numbered pixels, and red pixels and Green color becomes stronger because blue pixels become darker. As a result, magenta and green are alternately displayed every other row of picture elements, and the image quality is degraded.

  Therefore, in view of the above problems, the present invention provides an active matrix organic EL image display device capable of suppressing deterioration in image quality.

  An organic EL image display device according to the present invention includes a plurality of pixels arranged in a matrix on a substrate, a plurality of scanning lines and a plurality of signal lines arranged to cross each of the pixels. A plurality of power supply lines arranged in parallel with the signal line, and each pixel includes a first transistor to which a scanning signal from the scanning line is supplied and an image signal supplied from the signal line. In an image display device, comprising: a storage capacitor that holds the image signal; a second transistor to which the image signal held by the storage capacitor is supplied; and an organic EL element that emits light by a current supplied from the power supply line. In the plurality of pixels, pixel rows of odd-numbered colors are sequentially arranged in the extending direction of the scanning line, and the power supply line is common to pixel rows of two colors among the pixel rows of odd-numbered colors. Common power supply When, characterized by comprising a single feed line energizes one color pixel column of the.

  In the above invention, the image signal supplied from the signal line is preferably corrected for luminance for each color type.

  In the above invention, it is preferable that the second transistor includes a common second transistor formed across two color pixels in the odd-numbered color pixel column.

  Moreover, in the said invention, it is preferable that the pixel of the odd number of colors is three colors of red, green, and blue.

  In the above invention, it is preferable that the brightness correction unit corrects all pixels simultaneously.

  In the above invention, it is preferable that the circuit arrangement of the two-color pixels formed across the common power supply line is substantially line symmetric with respect to the common power supply line.

  Furthermore, in the above invention, it is preferable that the common second transistor is substantially line symmetric with respect to the common power supply line.

  According to the present invention, when pixel rows of odd-numbered colors are sequentially arranged, the change in luminance due to the characteristics of the transistor is also different for each pixel color type. Therefore, the appearance in units of picture elements is made uniform, so that deterioration in image quality can be suppressed. In addition, since correction can be performed for each color type, luminance correction can be easily performed.

  Hereinafter, an organic EL display device according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following description, In the range which does not deviate from the summary of this invention, it can change suitably. Further, the drawings are schematic diagrams for facilitating understanding of the present invention, and may differ from actual dimensions and scales.

  The “gate voltage” in this specification refers to a potential difference between a source and a gate with respect to the potential of the source with respect to the transistor. Further, the “threshold voltage of a transistor” in this specification refers to a gate voltage that becomes a boundary when a transistor changes from an off state (a state in which a drain current does not flow) to an on state (a state in which a drain current flows).

[First embodiment]
<Schematic configuration of image display device>
FIG. 1 is a diagram showing a schematic configuration of a portable electronic device 100 using an organic EL image display device 120 according to an embodiment of the present invention.

  The mobile electronic device 100 includes a main body 110 and an organic EL image display device 120. Although there is no particular limitation, the embodiment will be described by exemplifying a mobile phone. Various images such as moving images and still images are displayed on the organic EL image display device 120.

  The main body 110 includes a communication function, a power feeding function such as a battery, and an operation unit.

  The organic EL image display device 120 includes, for example, a display unit having a substantially rectangular outer shape including a plurality of organic EL elements and a driver unit to which various signals supplied from the main body unit 110 are input. Note that an organic EL element refers to a self-luminous light emitting element that emits light by flowing current through an organic material.

  The organic EL image display device 120 includes a signal line 30 and a scanning line 20. The signal line 30 supplies each pixel with a potential corresponding to an image signal corresponding to the light emission luminance (for example, a pixel data signal for each pixel). The scanning line 20 is provided so as to be substantially perpendicular to the image signal line, and supplies a scanning signal to each pixel. The scanning signal is a signal that controls the timing at which charges corresponding to the pixel data signal are accumulated in each pixel via the signal line.

  The driver means includes an X driver (image signal line drive circuit) Xd and a Y driver Yd. The X driver Xd is electrically connected to the signal line 30 and controls timing for supplying a potential corresponding to the image data signal to the signal line. The Y driver Yd is electrically connected to the scanning line 20 and controls the timing at which the scanning signal is supplied to the scanning line 20.

<Configuration of organic EL image display device>
FIG. 2 is a schematic diagram illustrating the functional configuration of the organic EL image display device 120 according to the first embodiment. The organic EL image display device 120 includes a control unit 70, an X driver Xd, a Y driver Yd, a display unit 10, and a power supply unit 50.

  The control unit 70 performs overall control of the operation of the organic EL image display device 120. The control unit 70 includes a CPU, a RAM, a ROM, and the like. For example, the CPU reads and executes a program stored in the ROM or the like, thereby realizing various operations and controls. The control unit 70 also has a function of controlling transmission of signals from the X driver Xd and the Y driver Yd.

  The display unit 10 has an active matrix type in which a plurality of pixels 80 are arranged in a matrix. The pixel 80 has an odd number of emission colors, specifically, three colors of red, green, and blue. The three pixels 80 constitute one picture element 90.

  An example of a pixel circuit in each pixel is shown in the upper left pixel in FIG. Although other pixels have similar pixel circuits, they are omitted in the drawing. The pixel circuit includes an organic EL element OLED, a first transistor Tth, a second transistor Td, and a storage capacitor Cs.

  The organic EL element OLED is a light emitting element that has a light emitting layer made of an organic material and the like, and whose luminance changes depending on the amount of current flowing through the light emitting layer. This organic EL element OLED has an anode electrode and a cathode electrode. The anode electrode is electrically connected to a power source that applies a relatively high voltage when the organic EL element emits light. On the other hand, the cathode electrode is connected to a power source that applies a voltage lower than the voltage applied to the anode electrode when the organic EL element emits light. In the present embodiment, the anode electrode is electrically connected to the power supply unit 50 via the feeder line 40, and the cathode electrode is connected to the power supply line 45 via the source-drain of the second transistor (drive transistor). Electrically connected. The power supply line 45 can be replaced with a ground.

  The first transistor Tth and the second transistor Td are thin film transistors (TFTs) which are a kind of field effect transistor (FET) adopting a MIS (Metal Insulator Semiconductor) structure of a type (n-type) in which carriers are electrons. Thin Film Transistor), that is, n-MISFETTET.

  The gate of the first transistor (threshold voltage detection transistor) Tth is electrically connected to the scanning line 20. One terminal serving as a source or drain is electrically connected to the holding capacitor Cs, and the other terminal is electrically connected to the cathode electrode of the organic EL element OLED and one terminal of the source or drain of the second transistor. The

  Further, the first transistor Tth adjusts the potential applied from the scanning line 20 to the gate, specifically, the voltage value applied between the gate and the source, whereby the amount of current flowing between the source and the drain is adjusted. Adjusted. Further, a state in which current can flow between the source and drain (energized state) and a state in which current cannot flow (non-energized state) are selectively set by the potential applied to the gate.

  The gate of the second transistor (driving transistor) Td is connected to the signal line 30 via the storage capacitor Cs. One terminal serving as a source or drain is connected to the power supply line 40 via the organic EL element OLED, and the other terminal is electrically connected to the power supply line 45. When the organic EL element OLED emits light, that is, when a forward current flows through the organic EL element OLED, one terminal functions as a drain and the other terminal functions as a source.

  In the second transistor Td, the potential applied to the gate, more specifically, the voltage value applied between the gate and the source is adjusted, so that the current flowing between the source and the drain is adjusted. Then, along with the adjustment of the amount of current flowing between the gate and the source, the amount of current flowing in the organic EL element OLED is controlled. In addition, the potential applied to the gate is selectively set to a state where current can flow between the source and drain (conductive state) and a state where current cannot flow (non-conductive state).

  Further, the second transistor Td has a gate voltage (specifically, a potential difference between the gate and the source with reference to the potential of the source in the conductive state of the second transistor Td) Vgs in the conductive state. There is a threshold voltage Vth of the second transistor.

  Here, since the light emission luminance of the organic EL element OLED is controlled by a current value, the light emission luminance of the first transistor Td during light emission varies sensitively with respect to the fluctuation of the gate voltage Vgs. In particular, when the second transistor Td is configured using amorphous silicon, the threshold voltage Vth tends to be different for each second transistor Td. Therefore, if the function of compensating the threshold voltage Vth that differs for each pixel (Vth compensation function) is not provided, there is a slight difference between the predetermined light emission luminance and the actual light emission luminance, and as a result, light emission between the pixels. Uneven brightness will occur.

  Therefore, in the organic EL image display device 120, the variation of the threshold voltage Vth in the second transistor Td is compensated by setting the gate voltage Vgs of the second transistor Td to a value corresponding to the threshold voltage Vth in each pixel before light emission. In order to realize the processing (Vth compensation processing), the first transistor Tth is provided. Specifically, first, the auxiliary capacitor Cs is charged, and then the first transistor Tth is turned on to connect the source and drain of the second transistor Td. As a result, the auxiliary capacitor Cs is discharged through Td, the gate potential of Td is lowered until it reaches the threshold voltage Vth, and the image signal voltage is added to Vth thus detected to compensate the threshold voltage Vth of the second transistor Td. To do.

The storage capacitor Cs has one electrode electrically connected to the signal line 30, and the other electrode electrically connected to either the source or the drain of the first transistor Tth and the gate of the second transistor Td. ing.

  The X driver Xd supplies a potential corresponding to the image signal to the signal line 30 in response to a signal from the control unit 70. Note that the control unit 70 sends, to the X driver Xd, a signal that controls the potential supply timing corresponding to the image signal to each signal line 30 from the X driver Xd in synchronization with, for example, image data transmitted from the outside. To do. Further, in the potential adjustment stage for causing the organic EL element OLED to emit light, the X driver Xd selects a predetermined reference potential and a predetermined high potential for the signal line 30 in response to a signal from the control unit 70. Is granted.

  The Y driver Yd gives a potential corresponding to the scanning signal to the scanning line 20 with a waveform corresponding to the control signal from the control unit 70.

  Further, the control unit 70 includes luminance correction means for correcting the luminance for each color of the pixel 80. Specifically, the current value or luminance flowing in the organic EL element corresponding to the pixel 80 of each color is measured during manufacturing or driving, and the controller 70 performs γ correction for each color type of the pixel, and the correction is performed. The performed image signal is supplied to each signal line 30 via the X driver Xd, and the luminance is corrected.

<Specific configuration of pixel>
3 and 4 are enlarged plan views showing the layout of the pixel circuit in the organic EL image display device according to the reference example. In the pixel circuit, a scanning line 20, a signal line 30, a power supply line 40, a power supply line 45, a first transistor Tth, a second transistor Td, and a storage capacitor Cs are arranged on a substrate. A planarizing film (not shown) made of an organic material is formed on the pixel circuit, and a light emitting layer (not shown) sandwiched between the anode electrode and the cathode electrode is formed on the planarizing film. Has been. In addition, what is attached | subjected with the same hatching has shown the same thing, and has abbreviate | omitted the code | symbol.

  The signal line 30 extends in the vertical direction in FIG. A portion where the width of the signal line 30 is formed functions as a storage capacitor Cs. The scanning line 20 extends in the left-right direction in FIG. 3 (that is, the direction intersecting with the signal line 30). Similarly to the signal line 30, the power supply line 40 extends in the vertical direction in FIG. 3 and is installed side by side with the signal line 30. A plurality of signal lines 30, scanning lines 20, and feeder lines 40 are arranged along each pixel. A signal and voltage from the signal line 30, the scanning line 20, and the power supply line 40 are applied to one pixel.

  A first transistor Tth is formed on the scanning line 20 of each pixel. The first transistor Tth is electrically connected to the light emitting layer through a contact portion 60 having a hole structure provided at one end in the planarization film. The other end is electrically connected to the electrode formed on the lower side.

A second transistor Td is formed on each feeder line 40. In addition, in the contact hole portion that connects the power supply line 40 and the electrode of the organic EL element OLED, the width of the power supply line 40 is formed wide. In the layout shown in FIG. In addition, since it is necessary to provide the power supply line 40, it is difficult to achieve pixel circuit arrangement and high functionality.

  Therefore, it is conceivable to lay out the pixel circuit as shown in FIG. In the layout, the circuit arrangement of every other pixel 80 is inverted in each pixel arranged along the arrangement direction of the scanning lines 20. In other words, the pixel circuits in the odd-numbered columns have a normal arrangement, and the circuit arrangement of the pixels in the even-numbered columns is substantially line symmetric (inverted arrangement) with respect to the feeder line 40.

  And it becomes possible to drive with one electric power feeding line 40 for every pixel group of two adjacent columns with the said layout. Therefore, compared with the case where one power supply line 40 is formed for each pixel group in one column, the formation region of the power supply line 40 on the substrate can be narrowed. Therefore, another circuit member can be arranged in the vacant space, and the degree of freedom in layout is improved. Furthermore, in the bottom emission type, since the issue area of the organic EL element OLED can be expanded, the luminance can be improved as compared with the layout shown in FIG.

  However, the layout shown in FIG. 4 has the following problems. The thin film transistors of the first transistor Tth and the second transistor Td are formed by photolithography, but when the photomask is misaligned during the formation of the thin film transistor, the characteristics of the normal pixel circuit and the inverted pixel circuit are different. Will be formed.

  In the case where the characteristics of the pixel circuit are different as described above, the pixel 80 has an odd-numbered color pixel, and the odd-numbered color pixel 80 constitutes one picture element 90. In some cases, the odd-numbered normal pixels 80 become bright and the pixels 80 in which the even-numbered pixel circuits are inverted become dark. An example is shown in FIG. FIG. 5 includes pixels 80 of three kinds of colors of red, green, and blue, and one picture element is configured from the pixels 80 of the three colors. Here, when the odd-numbered pixels 80 are in a normal arrangement and the even-numbered pixel circuits are in an inverted arrangement, it is assumed that the odd-numbered pixels 80 are bright and the even-numbered pixels 80 are dark. (Shown as A enclosed in dotted brackets).

  Then, when the pixels 80 arranged in the direction in which the scanning line 20 extends are shown in order, one picture element [red R (normal), green G (inverted), blue B (normal)], second picture element [Red R (reversed), green G (normal), blue B (reversed)]. In this case, when red single color display is performed, the odd-numbered picture elements become bright and the even-numbered picture elements 90 become dark, as shown in FIG. (The picture element 90 in the darkened column is shown as B surrounded by dotted brackets). Further, when white display is performed, the odd-numbered picture element 90 has bright red and blue pixels, and the green pixel is dark, resulting in a magenta color, and the even-numbered picture element 90 has a bright green pixel and red. Since the pixels and blue pixels become darker, green becomes stronger. As a result, magenta and green are alternately displayed every other row of picture elements, and the image quality is degraded.

  In order to prevent such deterioration in image quality, it is conceivable to correct the luminance of each pixel by γ correction or the like in the control unit 70. However, since the pixels 80 having different brightness reach a plurality of colors, it is difficult to improve the γ correction.

  Therefore, in the present embodiment, a pixel circuit layout as shown in FIG. 6 is used. In the layout, description of portions common to FIG. 3 is omitted. In the layout, odd-numbered color pixels 80 are sequentially arranged in the extending direction of the scanning lines 20. In addition, a common power supply line 42 that supplies power to pixels of two colors among odd-numbered colors of pixels and a single power supply line 41 that supplies power to pixels of one color are provided. More specifically, the pixel circuit of one type along the extending direction of the scanning line 20 is inverted substantially symmetrically with respect to the common power supply line 42 as a reference, and the first pixel [red R (normal) , Green G (normal), blue B (inverted)], second picture element [red R (normal), green G (normal), blue B (inverted)]...

  Therefore, in the present embodiment, the normal pixel 80 and the pixel 80 obtained by inverting the pixel circuit can be classified for each color type. Accordingly, as shown in FIG. 7, even if the pixel 80 of one color type becomes bright and the pixel 80 of the other color type becomes dark among the normal pixel 80 and the pixel 80 in which the pixel circuit is inverted (FIG. 7). In FIG. 8, C) surrounded by dotted parentheses, the risk of lowering the image quality for each picture element is reduced. Further, even when the pixel columns are compared with each other, since the same appearance is obtained, the problem that the image quality is deteriorated because vertical stripes are visible can be reduced.

  Further, since the change in luminance is for each color type of the pixel, the image quality can be further improved easily by performing γ correction for each color type in the control unit 70. That is, in the present embodiment, it is possible to improve the image quality while obtaining the effect of improving the luminance by reversing the pixels while realizing downsizing. Further, in this configuration, it is possible to correct all the pixels at the same time by the luminance correction means, and the correction time can be shortened. Further, since the correction can be simplified, it is preferable because the configuration of the luminance correction means can be facilitated.

  Further, in the present embodiment, as shown in FIG. 6, in the common power supply line 42, a common second line formed across two adjacent pixels, that is, a normal pixel 80 and an inverted pixel 80 is formed. Two transistors Td2 are provided. Thereby, the space on a board | substrate can be utilized effectively and the expansion of the further opening area | region (light emission area | region) of organic EL element OLED is attained.

  The common second transistor Td2 is preferably substantially line symmetric with respect to the common power supply line 42. As a result, a change in characteristics due to the positional deviation of the photomask during the formation of the thin film transistor is easily clarified between the normal pixel 80 and the inverted pixel 80, and the luminance correction in the control unit 70 is facilitated.

  The organic EL image display device according to the present invention can be used as a display unit of a portable information terminal such as a mobile phone or a personal computer. By using the present invention, it is possible to improve image quality while achieving downsizing and obtaining an effect of improving luminance by inversion of the pixel circuit.

It is the schematic of the electronic portable apparatus using the organic electroluminescent image display apparatus concerning one Embodiment of this invention. It is the schematic which illustrates the function structure of the organic electroluminescent image display apparatus concerning one Embodiment of this invention. It is an enlarged plan view which shows the layout of the pixel part in the organic electroluminescent image display apparatus concerning a reference example. It is an enlarged plan view which shows the layout of the pixel part in the organic electroluminescent image display apparatus concerning a reference example. It is the schematic which expanded three picture elements in a reference example. It is the schematic which shows the state in which the pixel in a reference example was arranged. It is an enlarged plan view which shows the layout of the pixel part of the organic electroluminescent image display apparatus concerning one Embodiment of this invention. It is the schematic which expanded three picture elements of the organic electroluminescent image display apparatus concerning one Embodiment of this invention. It is the schematic which shows the pixel circuit of the conventional organic EL image display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Portable electronic device 110: Main-body part 120: Organic EL image display apparatus Xd: X driver Yd: Y driver OLED: Organic EL element
Tth: first transistor (threshold voltage detection transistor)
Td: second transistor (drive transistor)
Td2: common second transistor Cs: holding capacitor 10: display unit 20: scanning line 30: signal line 40: power supply line 41: single power supply line 42: common power supply line 45: power supply line 50: power supply unit 70: control unit 80: Pixel 90: picture element

Claims (7)

A plurality of pixels arranged in a matrix on a substrate, a plurality of scanning lines and a plurality of signal lines arranged to cross each of the pixels, and a plurality of pixels arranged in parallel with the signal lines Power supply line, and
Each pixel is supplied with a first transistor to which a scanning signal from the scanning line is supplied, a holding capacitor for holding an image signal supplied from the signal line, and the image signal held by the holding capacitor. In an image display device comprising: a second transistor, and an organic EL element that emits light by a current supplied from the power supply line,
In the plurality of pixels, pixel rows of odd kinds of colors are sequentially arranged in the extending direction of the scanning lines,
The power supply line includes a common power supply line that supplies current to two color pixel columns and a single power supply line that supplies power to one color pixel column among the odd-numbered color pixel columns. An organic EL image display device.   The organic EL image display device according to claim 1, wherein the image signal supplied from the signal line is corrected in luminance for each color type.   3. The organic EL according to claim 1, wherein the second transistor includes a common second transistor formed across two color pixels in the odd-numbered color pixel column. Image display device.   The organic EL image display device according to any one of claims 1 to 3, wherein the pixels of the odd-numbered colors are three colors of red, green, and blue.   The organic EL image display device according to claim 1, wherein the luminance correction unit corrects all pixels simultaneously.   5. The organic EL image according to claim 1, wherein a circuit arrangement of the two color pixels formed with the common power supply line interposed therebetween is substantially line-symmetric with respect to the common power supply line. 6. Display device. The organic EL image display device according to claim 3, wherein the common second transistor is substantially line symmetric with respect to the common power supply line.

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